Abundance and spatial distribution of mosquitoes across three ecological zones of Ondo State. Nigeria

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1 2017; 4(5): ISSN: CODEN: IJMRK2 IJMR 2017; 4(5): IJMR Received: Accepted: Olajire Ayodele Gbaye Olajide Joseph Afolabi Iyabo Adepeju Simon-Oke Aminat Omolara Lasisi Abundance and spatial distribution of mosquitoes across three ecological zones of Ondo State Olajire Ayodele Gbaye, Olajide Joseph Afolabi, Iyabo Adepeju Simon- Oke and Aminat Omolara Lasisi Abstract The study was undertaken in three ecological zones of Ondo State to determine the abundance and spatial distribution of mosquitoes in the ecological zones of the state. Twenty (20) sampling sites randomly distributed across each of the zones were sampled using aspirators, dippers and pipettes. The results revealed 12 mosquitoes species belonging to 3 genera, these include 5 species of Culex (Cx. quinquefasciatus, Cx. andersoni, Cx. duttoni, Cx. pipiens and Cx. trigripis), 4 species of Aedes (Ae. aegypti, Ae. albopictus, Ae. vittatus and Ae. palpalis) and 3 species of Anopheles (An. gambiae, An. arabiensis and An. funestus). The study further showed that Cx. quinquefasciatus was the most predominant Culex species observed in Idanre and Ese Odo, while Cx. andersoni was the predominant Culex species in Ondo, Ifon and Ikare Akoko. Ae. aegypti was the most dominant in all the locations except Ese Odo. An. gambiae has the highest occurrence in all the ecological zones. The results of this study show that the area is rich in mosquitoes, and the abundance of the mosquitoes especially the An. gambiae is of public health importance. Keywords: Mosquitoes, Abundance, Physico-chemical parameters, Ecological zones Correspondence Olajide Joseph Afolabi 1. Introduction Mosquitoes are notorious insects which transmit many dreadful diseases causing critical health challenges to human. Diseases vectored by mosquitoes include: malaria, filariasis and yellow fever [1]. These diseases cause high morbidity and mortality in human. Despite progress made to combat malaria and mosquito related diseases, globally, about 3.2 million people are still at risk of malaria. In, malaria still remains one of the leading causes of childhood and maternal morbidity and mortality, low productivity and reduced school attendance [2]. was ranked as the highest country with malaria prevalence on the world malaria day in 2015 due to about 300,000 deaths which usually occur each year as a result of malaria [3]. Climatic factors such as temperature, rainfall and relative humidity are vital components of the ecosystem that regulate the population density of mosquitoes [4]. Temperature influences vector development rates, mortality and behaviour. Temperature can also interact with rainfall to regulate evaporation thereby affecting the availability of water habitats. Rainfall, temperature and humidity indirectly influence land cover and land use which can promote or disrupt vector populations. Climate change is one of the most important factors to be considered in vector ecology because it affects human health. The link between climate and diseases with various modes of transmission has been identified with the strongest association being between climate and mosquito-borne diseases [5]. Dengue fever has been associated with vegetation indices, tree cover, surrounding land cover and housing quality [6]. Transmission is associated with changes in temperature, rainfall, humidity as well as level of immunity. The IPCC Special Report on Regional Impacts of Climate Change [7] acknowledged that climate has an impact on vector-borne diseases. Changes in climate affect potential geographical distribution and transmission of vector-borne infectious diseases such as malaria. There are many substantial research challenges associated with studying linkages among climate, ecosystems, and infectious diseases. For instance, climate-related, such as rapid evolution of drug- and pesticide-resistant pathogens, swift global dissemination of microbes and vectors ~ 23 ~

2 through expanding transportation networks, and deterioration of public health programs in some regions. Proper understanding of the environmental factors that promote the breeding of mosquitoes becomes imperative for successful planning of mosquito control measures [8]. The study aim is to identify the predominant mosquito species in each ecological zone and show how the ecological vegetation and physicochemical parameters influence the abundant of mosquitoes in the study area. 2. Materials and methods 2.1 Study area This study was carried out in Ondo State, which is one of the States in the Western State of. The State comprises of three ecological zones: mangrove forest, rainforest and savannah forest. The locations sampled are Idanre, Ondo, Ifon, Ikare-Akoko and Ese-Odo. The tropical rainforest used was located in Idanre (Latitude of 7 o 10' and a Longitude 5 o 09' 00.1 ), Ifon in Ose (Latitude of 6 o 55' and a Longitude of 5 o 45' 4.70 ), Ondo East Local Government Area (Longitude 5 o E and Latitude 7 o N) with a mean annual rainfall of about 4000 mm and temperature range from about 20.6 o C to 33.5 o C. The derived savannah is chosen from Akoko North East Local Government Area (Ikare-Akoko) of Ondo State. It is located between longitude (5 o E and latitude 7 o N). The mean annual rainfall is about 3500mm and temperature ranges from 26 o C to 39 o C. Ese-Odo Local Government Area of Ondo State is a mangrove forest. It is on (Latitude 7 o N and longitude 5 o 'E). The climatic condition of the area is cold with sea breeze and it experiences a mean annual rainfall of about 400 mm to 450 mm which occurs normally between April to September and has its dry season from November to March. It has mean annual temperature of 28 o C. 2.2 Sampling, collection and identification of mosquito larvae Twenty (20) sampling sites randomly distributed across each of the zones were sampled using aspirators, dippers and pipettes from January 2015 to December The habitats sampled were: abandoned plastics, gutters, tanks, puddles, tree holes and used tyres. A hand dipper which is a white plastic cup with a volume of 350 ml attached to a handle was used to sample the mosquito population and the samples were concentrated through a small mesh screen using a concentrator cup. The samples were then preserved with 70% ethanol in plastic snap-cap vials with a volumetric capacity of ~ 55 ml and transported to the laboratory for identification. The larvae were identified to species level using dissecting microscope and guided by the morphological keys [9, 10, 11]. 2.3 Determination of the physico-chemical parameters The water sample where the larvae were harvested was analyzed for physicochemical parameters on the field. The parameters include temperature, ph, relative humidity, dissolved oxygen and electrical conductivity. Model 350 ph meter ( ) which is a portable battery operated meter was used to measure the ph, electrical conductivity of the water samples was measured using a portable battery operated conductivity meter (Model 470), dissolved Oxygen (DO 2) was measured using pre-calibrated dissolved oxygen meter (Model ) and portable thermo-hygrometer was used in measuring the temperature of all water samples and also the relative humidity of the environment. All data collected were analyzed using one way analysis of variance (ANOVA) and where there were significant differences, Tukey test at p<0.05 was used to separate the means using SPSS Results 3.1 Mosquito larval habitats and physico-chemical parameters of the sampled water in the ecological zones of Ondo State. Table 1 shows the types of mosquito larva collected per habitat in the three ecological zones in Ondo State. The habitats in which mosquito breeding was found include abandoned plastics, puddles, gutters, tyres, tanks and tree holes. Puddles made up the largest breeding site (22.24%) while tree holes made up lowest breeding site (6.68%). Puddles (176), gutters (165) and tree holes (87) were most abundant in Ese-odo (mangrove forest) while abandoned plastics (166), tyres (140) and tanks (163) were most abundant in Ondo, Ikare-Akoko and Idanre respectively. From the result in Table 2, it was observed that temperature, relative humidity, ph, electrical conductivity and dissolved oxygen are the major factors that could play an important role in breeding and propagation of mosquitoes. Table 2 shows the result of the physicochemical parameters conducted on the water where the mosquito larvae were collected. The result shows that dissolved oxygen (ppm/mgl) of the water from Idanre (2.06±0.02ppm/mgl) was not significantly different from that of Ifon (2.06±0.02ppm/mgl) but the dissolved oxygen from Idanre and Ifon were significantly different from those collected from Ondo (1.95±0.12ppm/mgl), Ikare-Akoko (2.36±0.01ppm/mgl) and Ese-odo (2.67±0.12ppm/mgl) respectively (P<0.05). The highest dissolved oxygen (2.67±0.12ppm/mgl) in the ecological zones was obtained in Ese-odo; a mangrove forest in Ondo State. Meanwhile, the least dissolved oxygen (1.95±0.12ppm/mgl) was obtained in Ondo; a rainforest area of Ondo State. Similarly, the highest electrical conductivity (209.33±2.42 µs/cm) in the study area was observed in Ikare-Akoko; a derived savannah while the least electrical conductivity (92.03 ±0.24µs/cm) was observed in Ese-odo; a mangrove forest. It was further observed that the electrical conductivity of Ese-odo was not significantly different from that of Ondo (96.49 ±0.23µs/cm). Table 2 also shows that the breeding temperature varies from one ecological zone to another. For instance, highest temperature (27.22 ± 0.53 o C) of the breeding water was observed in Idanre; a rainforest while the least breeding temperature (25.09 ± 0.03 o C) was noted in Ese-odo; a mangrove forest. The breeding temperature in Ikare-Akoko (26.25 ± 0.07 o C)); a derived forest was significantly different from that of rainforest and mangrove forest (P<0.05). It was also observed in the study that the relative humidity where mosquito breeding was observed were not significantly different (P>0.05) from rainforest (Idanre, Ondo and Ifon) to derived savannah (Ikare-Akoko) but the relative humidity of the mangrove forest (Ese-odo) where the highest relative humidity (76%) was recorded was significantly different from other ecological zones (P<0.05). It was further observed from Table 2 that the ph of breeding water in Idanre (7.15) was not significantly different from that of Ondo (7.13± 0.00). Also,

3 that of Ifon (7.07 ± 0.00) and Ikare-Akoko (7.07 ± 0.02) were not significantly different from each other (P>0.05). The physicochemical range where mosquito breeding was observed in the ecological zone include dissolved oxygen range of 1.95 ± ± 0.12ppm/mgl, electrical conductivity range of ± ± 2.42µs/cm, temperature range of ± ± 0.53 o C, relative humidity range of ± ± 1.12% and ph range of 7.07 ± ± Table 1: Total number of mosquito larvae obtained at different breeding sites. Locations Abandoned Plastics Puddles Gutters Tyres Tanks Tree holes Idanre Ondo Ifon Ikare-Akoko Ese-odo Total Percentage (%) Table 2: Physico-chemical parameters of the mosquito breeding water in different ecological zones of Ondo State. Locations DO EC TEMP RH ph Idanre 2.06±0.02 b ±3.18 c 27.22±0.53 d 62.67±1.15 a 7.15±0.01 b Ondo 1.95±0.12 a 96.49±0.23 a 26.96±0.01 c 63.67±0.87 ab 7.13±0.00 b Ifon 2.06±0.02 b ±0.79 b 26.97±0.02 c 66.67±1.05 b 7.07±0.00 a Ikare 2.36±0.01 c ±2.42 d 26.25±0.07 b 62.67±1.25 a 7.07±0.02 a Ese-odo 2.67±0.12 e 92.03±0.24 a 25.09±0.03 a 76.00±1.12 c 7.24±0.00 c Mean followed by the same letter along the column are not significantly different using (p>0.05) Tukey s Test. KEYS: DO Dissolve Oxygen (ppm/mgl); EC Electrical Conductivity (µs/cm); Temp Temperature ( o C); RH Relative humidity (%). 3.2 Abundance and distribution of mosquito larvae in the ecological zones of Ondo State The results in Table 3-5 showed that most of the species and number of larvae collected across the zones were significantly different (P<0.05). Cx. quinquefasciatus was the most abundant species in Ese-odo (50.67±2.03) while Cx. quinquefasciatus and Cx. andersoni were the most abundant in Idanre, Ondo, Ifon and Ikare-Akoko respectively (Table 3). The least abundant mosquito species were Cx. tigripis (4.00±4.00) in Idanre and Ikare-Akoko (20.00±5.03) while the species was completely absent in Ifon and Ese-odo. Similarly, Cx pipiens was not encountered in Ondo and Ifon. Cx. quinquefasciatus, Cx. andersoni and Cx. duttoni were evenly distributed in all the three ecological zones as these species were encountered in the three ecological zones while Cx. trigripis was not encountered in Ifon and Ese-odo, and Cx. pipiens was completely absent in Ondo and Ifon (Table 3). Table 4 shows the abundance and distribution of Aedes spp across the ecological zones. Four species of Aedes were identified from the study area, these include Ae. aegypti, Ae. albopictus, Ae. vittatus and Ae. palpalis. All these species with the exception of Ae. palpalis were observed in all the ecological zones. But Ae. palpalis was absent in Idanre and Ondo. It was also noted that the abundance of Ae. aegypti, Ae. albopictus and Ae. vittatus were not significantly different in the freshwater ecological zones (Idanre, Ondo and Ifon) while the abundance of Ae. aegypti (68.33±8.09) in Ikare-Akoko (derived savannah) was significantly different from other Aedes spp from the same location (Table 4). In Table 5, three species of genus Anophelinae were observed: An. gambiae, An. arabiensis and An. funestus. But the abundance of An. gambiae was the highest in all the ecological zones. Notably, An. arabiensis was absent in Ifon, Ikare-Akoko and Ese-odo, and An. funestus was not encountered in Idanre and Ondo which are freshwater ecological zones. In general, An. gambiae, a notable malaria mosquito in was the most abundant species of mosquitoes in all the ecological zones. This species was also evenly distributed across the three ecological zones studied in this research. Table 3: Abundance and distribution of Culex mosquitoes in ecological zones of Ondo State. Culex quinquefasciatus 69.33±9.96 c 2.33±8.41 b 42.33±8.65 bc 43.33±4.91 b 50.67±2.03 e Culex anderson 59.33±7.51 bc 56.67±8.29 b 59.00±10.44 c 61.67±9.94 b 32.00±2.31 c Culex duttoni 21.67±1.45 a 36.67±5.78 b 23.33±4.49 b 20.00±5.03 a 13.67±1.45 b Culex tigripis 4.00±4.000 a 6.00±6.00 a 0.00±0.000 a 20.00±5.03 a 0.00±0.000 a Culex pipiens 8.00±5.29 a 0.00±0.000 a 0.00±0.000 a 44.00±4.62 b 42.00±4.36 d Mean followed by the same letter along the column are not significantly different using (p>0.05) Tukey s Test 25

4 Table 4: Abundance and distribution of Aedes mosquitoes in ecological zones of Ondo State. Aedes aegypti 56.67±8.67 b 51.33±12.24 b 59.33±10.53 b 68.33±8.09 c 43.00±9.71 ab Aedes albopictus 52.67±5.70 b 43.67±10.11 b 55.33±9.77 b 24.67±5.46 ab 82.33±22.06 b Aedes vittatus 46.00±6.43 b 40.67±8.97 b 49.67±8.41 b 37.67±8.84 b 47.67±3.84 ab Aedes palpalis 0.00±0.000 a 0.00±0.000 a 13.33±2.60 a 13.33±2.60 a 31.67±4.10 a Table 5: Abundance of Anopheles mosquitoes in ecological zones of Ondo State. Anopheles gambiae 83.00±4.93c 89.33±9.62a 82.67±21.86b 87.00±19.52b 82.67±21.86b Anopheles arabiensis 36.00±6.11b 51.33±12.24b 0.00±0.000a 0.00±0.000a 0.00±0.000a Anopheles funestus 0.00±0.000a 0.00±0.000a 23.67±4.26a 18.00±3.00a 31.67±12.09a 4. Discussion The study area was rich in mosquitoes, mosquitoes breed virtually in all habitats sampled which were ground pools, domestic containers, tanks, tyres, tree holes, gutters and manmade containers which were the main breeding sites for mosquitoes. These breeding sites are common in the study area as a result of human activities, poor economic conditions; low literacy levels, poor sanitation level and indiscriminate disposal of discarded household materials which results in abundance of pools, ponds, puddles, water collections in tins, bowls, drums, clay pots and tree holes. Drums, clay pots and bucket containers of various sizes are used for domestic water collection during raining season. These water containers are sited around human dwellings where adult female mosquitoes can oviposit and subsequently breed its pre-adult stages (larvae and pupae). The physico-chemical parameters of these breeding habitats were noted to be favorable for mosquito breeding. The dissolve oxygen (DO 2) of the water collected from the rainforest was between the range of ( ppm/mgl) while that of Ikare-Akoko was 2.36 ppm/mgl and that of Eseodo is 2.67 ppm/mgl. Generally, the DO 2 of the studied areas was low ( ). This might be because of the discharge of agricultural wastes, domestic wastes and organic material into water body. The survival of larvae when submerged depends on their ability to absorb oxygen through the cuticle. When the level of DO 2 is low the rate of loss of buoyancy is said to be rapid, this suggests that the outward diffusion of gas into the water is significant. This might be the reason why there is abundance of Cx. quinquefasciatus when the DO 2 was low because it has the ability to survive for considerable longer period than any other species. The electrical conductivity of the water sampled in Idanre, Ondo and Ifon were close to each other but Ikare-Akoko has the highest electrical conductivity (209 µs/cm) while Ese-odo has the lowest (92 µs/cm). Ese-odo has the highest relative humidity of 76% while Ikare-Akoko and Idanre has a relative humidity of 62%, Ifon was 66% and Ondo was 63.% The ph recorded in the studied area were slightly alkaline ( ) and this might have resulted in the abundance of mosquitoes in the studied areas. This is because most mosquito species thrive better in alkaline environment. Similar result has been reported by Afolabi et al. [12]. The authors reported that almost all the alkaline ph (ph >7) favored the breeding of mosquitoes in Akure,. The ph of Ese-odo is tending toward alkalinity (7.24) this might be as a result of the area being riverine. Ese-odo has the lowest temperature of 25 o C while Idanre has the highest (27 o C). The dissolve oxygen, humidity and temperature of water are 26 the main factors that influence the abundance and distribution of mosquito larva in the aquatic habitats. The temperature range in which mosquito breeding was found in the study area is o C. This suggests that temperature range of o C is suitable for mosquito breeding in the study area. This report agrees with the reports given by Adebote et al. [13] and Afolabi and Ndams [4]. The authors in their separate studies in Zaria, reported that temperature below 24.7 o C and above 28.3 o C are fatal to mosquito species. and also that there is inverse relationship between mosquito abundance and temperature as the temperature increases from 24.7 to 29 o C. The three ecological zones studied (tropical rainforest, derived savanna and mangrove forest) are favorable for breeding mosquito larvae. In terms of species richness, Ikare- Akoko; a derived savannah with 11 species was the richest ecological zone followed closely by Idanre and Ese-odo with 10 species each. Ondo and Ifon with 9 species each were the least. Of the 12 species of mosquito encountered in the study area only An. arabiensis was absent in Idanre. This suggests that the physico-chemical parameters such as dissolved oxygen (2.36ppm/mgl), electrical conductivity (209.33µs), relative humidity (62.67%), temperature (26.25 o C) and ph 7.07 are most favorable for the breeding of mosquitoes in derived savannah. The absence of An. arabiensis in derived savannah (Idanre) and mangrove forest (Ese-odo) might be because of the relative low temperature ( o C) in the ecological zone. Contrary, An. arabiensis was present in the rainforest (Idanre and Ondo) where temperature is relatively high ( o C). The rainforest are usually characterized with high temperature and water. Similarly, all the four species of Aedes with the exception of Ae. palpalis favorably breed in all the ecological zones. Meanwhile, Ae. palpalis larvae were not encountered in rainforest (Idanre and Ondo) but present in derived savannah (Ikare-Akoko) and mangrove forest (Ese-odo). This shows that Ae. palpalis and An. arabiensis share the same temperature range. Cx. quinquefasciatus, Cx. andersoni and Cx. duttoni were encountered in all the ecological zones while Cx. tigripis were completely absent in Ifon and Ese-Odo, even in areas (Idanre- 4, Ondo-6 and Ikare-Akoko-20) where it was found breeding, the abundance was very low. This suggests that the ecological zones in Ondo State do not favor the breeding of this species. Likewise, Cx. pipiens was observed to breed better in derived savannah (Ikare-Akoko) and mangrove forest (Ese-odo) than the rainforest (Idanre, Ondo and Ifon). For instance Cx. pipiens was completely absent in Ondo and Ifon but breed at a very low abundance (n=8) in Idanre.

5 5. Conclusions The results of this study show that the area is rich in mosquitoes, and the abundance of the mosquitoes is attributable to the presence of favorable physico-chemical parameters such as temperature, relative humidity, ph, electrical conductivity and dissolved oxygen. Mosquitoes were observed to breed virtually in all habitats sampled which were ground pools, domestic containers, tanks, tyres, tree holes, gutters and manmade containers. These breeding sites are common in the study area as a result of human activities, poor economic conditions; low literacy levels, poor sanitation level and indiscriminate disposal of discarded household materials which results in abundance of pools, ponds, puddles, water collections in tins, bowls, drums, clay pots, tree holes drums and bucket containers of various sizes used for domestic water collection during raining season. The findings of this study suggest removal of smaller man-made aquatic habitats like abandoned plastics, cans, puddles and tyres could bring about effective larval control of mosquitoes in the study areas. In Idanre, tanks, gutters and puddles should be targeted while controlling mosquito larvae to achieve effective larval control while abandoned plastics, puddles and tyres should be targeted in Ondo. Abandoned plastics should be cleared and recycled, puddles should be drained and gutters should be cleared to control mosquito larva in Ifon. In Ikare-Akoko, tyres, abandoned plastics and gutters should be targeted while puddles, gutters and tyres should be targeted for effective larval control in Ese-Odo. Johannesburg, South Africa, Izdihar K, Ibrahim B, Total YM, Mehsin AZ, Salan K. Identification key for Iraqi Culicine mosquito larva (Culicine-Diptera). Bulletin of Endemic Diseases. 1983; 8: Pirkka U. Identification key to finish mosquito larva (Diptera, Culicidae). Annales Agriculturae fenniae, 1976; 15: Afolabi OJ, Simon-Oke IA, Osomo BO. Distribution, abundance and diversity of mosquitoes in Akure, Ondo State.. Journal of Parasitology and Vector Biology. 2013; 5(10): Adebote DA, Oniye SJ, Muhammed YA. Studies on mosquitoes breeding in rock pools in Inselbergs around Zaria. Northern. Journal of Vector Borne Disease. 2008; 45(1): Afolabi OJ, Ndams IS. The effects of climatic factors on the distribution and abundance of mosquitoes in phytotelmata. Journal of Medical and Applied Biosciences. 2010; 2: References 1. Dawn HG, Kirk AS, Carl O, Paul B. Cooperative extension, College of Agriculture and Life Sciences, The University of Arizona, Aribodor DN, Njoku OO, Eneanya CI, Onyali IO. Studies on prevalence of malaria and management practices of Azia community in Ihiala L.G.A, Anambra state. S.E.. n Journal of Parasitology. 2003; 24: World Health Organization. Indicator Cede Book. World Health Statistics-World 2015 (Health Statistics Indicator (Accessed ). 4. Ebi KL, Hartman J, Chan N, McConnell J, Schlesinger M, Weyant J. Climate suitability for stable malaria transmission in Zimbabwe under different climate change scenarios. Journal of Climate change. 2005; 73: Troyo A, Fuller DO, Calderon-Arguedes O, Solano ME, Bier JC. Urban structure and dengue fever in Punturenas, Coata Rica. Singap. Journal of Tropical Geography. 2009; 30: IPCC. The scientific basis. Contribution of working group 1 to the third assessment report of the intergovernmental panel on climate change. University press, Cambridge United Kingdom and New York. 2001, Monsuru AA, Wasiu OA, Abdul-Wasiu OH, Sunday OO, Ismail O, Ganiyu OO et al. Larval habitats of mosquito fauna in Osogbo metropolis, South western. Asian PAC Journal of Tropical Biomed Gillies MT, de Mellion. The Anophelinae of African South of the Sahara (Ethiopian Zoogeographical Region). The South African Institute for Medical Research. 27